Field of the Invention
The present invention relates to an image display apparatus and a control method thereof.
Description of the Related Art
Recently as the light receiving performance of imaging apparatuses improve, photographed image data having a wider dynamic range than BT. 709, which is normally used for video gamma, has begun to be generated. Hereafter image data having a wide dynamic range is referred to as “high dynamic range (HDR) image data”. For example, Cineon Log, determined based on the characteristics of films having a wide dynamic range, is used as a data format of HDR image data. In the workflow of image creation, HDR image data, which is photographed image data, is displayed on an image display apparatus during photographing, and the signal level confirmation and color adjustment are performed for the imaging apparatus based on the display result.
In an image display apparatus, on the other hand, a displayable dynamic range (display range) may be limited to a dynamic range narrower than the dynamic range of an imaging apparatus (photographing range) in some cases, considering an increase in power consumption, drop in reliability caused by component heating and the like. In this case, image data of which dynamic range is wider than the display range is displayed after image processing to narrow the dynamic range to the display range (compression processing) is performed. If compression processing is performed on image data, general brightness of the display image (image displayed on screen) drops, and visibility of the display image deteriorates.
Prior arts related to the compression processing are disclosed, for example, in Japanese Patent Application Laid-Open No. 2004-220438 and Japanese Patent Application Laid-Open No. 2006-333113. According to the technique disclosed in Japanese Patent Application Laid-Open No. 2004-220438, the gradation width in a high brightness region in the image is compressed by the compression processing. According to the technique disclosed in Japanese Patent Application Laid-Open No. 2006-333113, a plurality of image data, of which degree of compression is different from each other, is created by performing a plurality of types of compression processing, of which control parameters related to the contrast and dynamic range are different from each other, on the image data. Then the generated plurality of image data is simultaneously displayed on one screen.
However, in the case of the technique disclosed in Japanese Patent Application Laid-Open No. 2004-220438, a difference is generated in the gradation characteristics between a high brightness region and the other image regions. In the case of the technique disclosed in Japanese Patent Application Laid-Open No. 2006-333113, a plurality of image data is simultaneously displayed on one screen, hence the image data cannot be displayed dot by dot. In other words, image quality deteriorates.
When the signal level confirmation and color adjustment are performed for an imaging apparatus based on the display result (display image) during photographing, it is preferable to display image data in which the gradation characteristics of the photographed image data are accurately reproduced. If the focus of the imaging apparatus is also confirmed at the same time, then it is preferable to display the image data dot by dot. In other words, it is preferable that the deterioration of the image quality is minimal (or not generated). This means that it is not desirable to use the techniques disclosed in Japanese Patent Application Laid-Open No. 2004-220438 and Japanese Patent Application Laid-Open No. 2006-333113 to confirm a photographed image data.